Project Summary The goal of the parent funded award (DP1DA044359 - ?The Epigenome in Substance Abuse Disorders: Engineering New Tools to Dissect Function from Form?) is to engineer molecular and cellular tools to control locus-specific DNA methylation in human neuronal cell culture and organoid models of the mesolimbic pathway. By controlling DNA methylation at specific genomic loci, functional questions can be asked about the role of DNA methylation in regulating persistent gene expression changes observed in response to chronic cocaine exposures. Interestingly, and highlighting its broad roles, DNA methylation patterns across the genome are also the best predictor of biological age. The hypothesis driving this Supplement proposal is that aged phenotypes in experimental models can be artificially induced by ectopically establishing DNA methylation patterns mimicking those of aged cells and tissues. Being able to control the age of experimental models would have strong potential in creating more relevant models of addiction as well as explore age-dependent modes of addiction. This is particularly important in developing human models of addiction, as human stem-cell derived systems often maintain relatively immature neuronal identities. Yet despite its strong impact on addiction research, there is likely a much greater potential impact of such artificially aged experimental models on our ability to study diseases such as Alzheimer's disease and its related dementias where age is the major risk factor, especially for majority idiopathic and sporadic versions of the disease. Here we propose to repurpose the same molecular and cellular tools engineered for the parent funded award, and apply them to control DNA methylation states in human stem cell-derived models to artificially age neurons and to study age-related neurodegeneration and the initiation and progression of ADRD phenotypes.